Touch sensing device and driving method thereof

ABSTRACT

A touch sensing device includes a panel including pixels disposed in a matrix form defined by data lines and gate lines, the pixels including thin film transistors (TFTs). The touch sensing device includes at least one touch sensor having a mutual capacitance and a sensor driving circuit configured to receive an electric charge from the mutual capacitance. The touch sensing device further includes a display driving circuit configured to supply a first parasitic capacitance suppressing signal to the data lines and a second parasitic capacitance suppressing signal to the gate lines during a touch sensor driving period.

The present invention claims the benefit of Korean Patent ApplicationNo. 10-2014-0129607 filed in Korea on Sep. 26, 2014, the entire contentsof which is incorporated herein by reference for all purposes as iffully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a touch sensing device and a drivingmethod thereof, and more particularly to a touch sensing device in whichtouch sensors are embedded in a pixel array, and a driving methodthereof.

2. Discussion of the Related Art

User interfaces (UIs) allow human beings (users) to communicate withvarious electric and electronic devices to easily control them asintended. Typical user interfaces include a keypad, a keyboard, a mouse,an on-screen display (OSD), a remote controller having an infraredcommunication or radio frequency (RF) communication function, and thelike. UI technologies are advancing toward enhancement of user emotionand operational convenience. Recently, UIs have evolved to a touch UI, avoice recognition UI, a 3D UI, and the like.

The touch UI is often employed in portable information devices such assmartphones and is increasingly applied to notebook computers, computermonitors, home appliances, and the like. Recently, a technique ofembedding touch sensors in a pixel array of a display panel(hereinafter, referred to as an “in-cell touch sensor”) has beenproposed. According to the in-cell touch sensor technique, touch sensorsmay be installed in a display panel without increasing the thickness ofthe display panel. The touch sensors are connected to pixels throughparasitic capacitances and signal lines (hereinafter, referred to as“pixel signal lines”). As for a driving method thereof, a period duringwhich pixels are driven (hereinafter, referred to as a “display drivingperiod”) and a period for driving touch sensors (hereinafter, referredto as a “touch sensor driving period”) are temporally divided in orderto reduce a mutual influence due to coupling between the pixels and thetouch sensors.

In the in-cell touch sensor technique, electrodes connected to pixels ofa display panel are utilized as electrodes of the touch sensors. Forexample, the in-cell touch sensor technique may include a method ofdividing a common electrode, for supplying a common voltage to pixels ofa liquid crystal display, for use as an electrode of the touch sensors.

As an example of a capacitance-type touch sensor that can be implementedas an in-cell touch sensor, a mutual capacitance-type touch sensor(hereinafter, referred to as a “touch sensor”) has been known.

FIGS. 1 and 2 are a plan view illustrating an electrode pattern of atouch sensor and an equivalent circuit diagram of the touch sensor,respectively.

As shown in FIGS. 1 and 2, a mutual capacitance-type touch screenincludes transmission (Tx) lines Tx1 to Tx4 and reception (Rx) lines Rx1to Rx4 intersecting the Tx lines Tx1 to Tx4 with dielectric materials(or insulating layers) interposed therebetween. A mutual capacitance Cmis formed between the Tx lines Tx1 to Tx4 and the Rx lines Rx1 to Rx4.When a touch driving signal (or a stimulating signal) is supplied to theTx lines Tx1 to Tx4, electric charges are charged in the mutualcapacitance Cm. A sensing circuit senses a touch input based on theamount of change in electric charges of the mutual capacitance Cm beforeand after the touch.

In FIG. 2, R(Tx) is a resistor of a Tx line, R(Rx) is a resistor of anRx line, C(Tx) is a parasitic capacitance of the Tx line, and C(Rx) is aparasitic capacitance of the Rx line.

When touch sensors are embedded in a pixel array, a large amount ofparasitic capacitances affecting the touch sensors due to couplingbetween the touch sensors and pixel signal lines is added. The pixelsignal lines are signal lines for writing data to pixels. In FIG. 3,pixel signal lines include a data line DL for supplying a data voltageto pixels and a gate line GL supplying a gate pulse (or a scan pulse)for selecting data-written pixels. In FIG. 3, Cfinger is a capacitanceequivalently expressing a finger when the finger applies a touch. Clc isa capacitance equivalently expressing a liquid crystal cell. Cdg is aparasitic capacitance between the gate line GL and the data line DL, andCgs is a parasitic capacitance between a gate and a source of a thinfilm transistor (TFT).

Parasitic capacitances connected to in-cell touch sensors include Ctd,Ctg, Ctc, Cgc, Cdc, and the like, as shown in FIG. 3. Ctd is a parasiticcapacitance between the Tx line and the data line DL, Ctg is a parasiticcapacitance between the Tx line and the gate line GL, Ctc is a parasiticcapacitance between the Tx line and the Rx line, Cgc is a parasiticcapacitance between the Rx line and the gate line GL, and Cdc is aparasitic capacitance between the Rx line and the data line DL. As asize of a touch screen employing in-cell touch sensors increases andresolution thereof increases, the touch sensitivity and touchrecognition accuracy declines due to parasitic capacitances connected tothe in-cell touch sensors. Thus, in order to apply the in-cell touchsensor technology to touch screens of a large-screen display device, theparasitic capacitance of touch sensors needs to be reduced or minimized.

FIG. 4 is a waveforms illustrating driving signals of a display device,such as that the one illustrated in FIG. 3.

As shown in FIG. 4, in order to drive a display device including in-celltouch sensors, a display driving period Td and a touch sensor drivingperiod Tt are temporally divided. During the display driving period Td,a data voltage Vdata and a gate pulse GP are generated to write data topixels. The gate pulse GP is swung between a gate high voltage VGH and agate low voltage VGL. During the display driving period Td, Tx lines andRx lines of touch sensors serve as a common electrode supplying a commonvoltage Vcom to the pixels. During the touch sensor driving period Tt, avoltage of the data lines DL is held at the final data voltage of theprevious display driving period Td and a voltage of the gate lines GL isheld at a gate low voltage VGL. During the touch sensor driving periodTd, a touch driving signal Tdrv is supplied to the Tx lines. During thetouch sensor driving period Td, the sensing circuit is insynchronization with the touch driving signal Tdrv and senses avariation in electric charges of the touch sensors through the Rx lines.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a touch sensing deviceand a driving method thereof that substantially obviate one or more ofthe problems due to limitations and disadvantages of the related art.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a touchsensing device includes: a panel including pixels disposed in a matrixform defined by data lines and gate lines, the pixels including thinfilm transistors (TFTs); at least one touch sensor having a mutualcapacitance; a sensor driving circuit configured to receive an electriccharge from the mutual capacitance; and a display driving circuitconfigured to supply a first parasitic capacitance suppressing signal tothe data lines and a second parasitic capacitance suppressing signal tothe gate lines during a touch sensor driving period.

In another aspect, a touch screen display device includes: a displaypanel including at least one touch sensor having a mutual capacitanceand pixels disposed in a matrix form defined by data lines and gatelines, the pixels including thin film transistors (TFTs); a sensordriving circuit configured to receive an electric charge from the mutualcapacitance; and a display driving circuit configured to supply a datavoltage of an input image to the data lines and a gate pulse to the gatelines during a display driving period, and to supply a first parasiticcapacitance suppressing signal to the data lines and a second parasiticcapacitance suppressing signal to the gate lines during a touch sensordriving period.

In yet another aspect, a method of driving a touch sensing device havinga panel with at least one touch sensor and pixels disposed in a matrixform defined by data lines and gate lines is disclosed. The methodincludes: supplying a first parasitic capacitance suppressing signal tothe data lines and a second parasitic capacitance suppressing signal tothe gate lines; determining a remaining amount of electric charge in thepanel; and if the remaining amount of electric charge exceeds athreshold amount, modifying a voltage level of at least one of the firstand second parasitic capacitance suppressing signals based on theremaining parasitic capacitance.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is an enlarged plan view of an electrode pattern of a mutualcapacitance-type touch sensor;

FIG. 2 is an equivalent circuit diagram of the touch sensor illustratedin FIG. 1;

FIG. 3 is a circuit diagram illustrating parasitic capacitances betweenin-cell touch sensors and pixels formed in a display device;

FIG. 4 is a waveform illustrating driving signals of the display deviceof FIG. 3;

FIG. 5 is a block diagram schematically illustrating a display deviceaccording to a first example embodiment of the present invention;

FIG. 6 is a plan view illustrating a structure of a touch screenincluding mutual capacitance touch sensors according to an exampleembodiment of the present invention;

FIG. 7 is a view illustrating sensor electrodes connected to a pluralityof pixels according to an example embodiment of the present invention;

FIG. 8 is a waveform view illustrating a method of time division drivingof pixels and touch sensors according to an example embodiment of thepresent invention;

FIGS. 9 and 10 are views illustrating a driving method of a touchsensing device according to an example embodiment of the presentinvention;

FIG. 11 is a detailed circuit diagram illustrating a driving circuit ofa display device according to an embodiment of the present invention;

FIG. 12 is an example waveform illustrating a pixel driving signal and atouch driving signal output from the driving circuit of FIG. 11;

FIG. 13 is a flow chart illustrating a process of generating a parasiticcapacitance suppressing signal according to an example embodiment of thepresent invention;

FIG. 14 is a circuit diagram illustrating an example embodiment of asensing circuit;

FIG. 15 is a view illustrating a configuration of a touch sensing deviceaccording to a second example embodiment of the present invention;

FIG. 16 is a schematic view illustrating a connection between a touchsensor Ts and a sensing unit 130 of a display panel according to thesecond example embodiment of the present invention; and

FIG. 17 is an equivalent circuit diagram illustrating parasiticcapacitances in a self-capacitance sensor structure according to anexample embodiment of the present invention.

DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Throughout the specification, like reference numerals refer tolike elements.

Names of elements used in the following description are selected for thedescription purpose and may be different from those of actual products.

A display device according to an example embodiment of the presentinvention may be implemented as a flat display device such as a liquidcrystal display (LCD), a field emission display (FED), a plasma displaypanel (PDP), an organic light emitting display (OLED), anelectrophoresis display (EPD), and the like. In the embodimentsdescribed hereinafter, a liquid crystal display (LCD) will be largelydescribed as an example of a flat display device, but the presentinvention is not limited thereto. For example, the display deviceaccording to example embodiments of the present invention may be appliedto any display device to which an in-cell touch sensor technology isapplicable.

A touch sensing device according to an example embodiment of the presentinvention includes a plurality of touch sensors embedded in a pixelarray by dividing a common electrode supplying a common voltage topixels. In order to minimize an influence of parasitic capacitancesconnected to in-cell touch sensors, an alternating current (AC) signalin phase with a touch driving signal is supplied to pixel signal lines.Also, an AC signal in phase with a touch driving signal may be appliedto Rx lines.

A common voltage Vcom applied to the pixels of the LCD is illustrated asa common voltage in example embodiments described hereinafter, but thepresent invention is not limited thereto. For example, the commonvoltage may be interpreted as a voltage commonly supplied to pixels of aflat display device, such as high potential/low potential sourcevoltages (VDD/VSS), or the like, commonly applied to pixels of anorganic light emitting diode display device.

In the touch sensing device according to example embodiments of thepresent invention, in a state in which sensor electrodes are connectedby short-circuiting touch sensors during a display driving period byusing switching elements, a common voltage Vcom may be supplied to thepixels through the connected sensor electrodes. In the touch sensingdevice according to example embodiments of the present invention, in astate in which the touch sensors are separated by turning off switchingelements during a touch sensor driving period, a touch driving signalmay be supplied to the touch sensors.

FIGS. 5 and 6 are block diagrams schematically illustrating a displaydevice and touch sensors according to a first example embodiment of thepresent invention. FIG. 7 is a view illustrating sensor electrodesconnected to a plurality of pixels according to the first exampleembodiment of the present invention. FIG. 8 is a waveform viewillustrating a method of time division driving of pixels and touchsensors according to the first example embodiment of the presentinvention.

As shown in FIGS. 5 through 8, the display device according to the firstexample embodiment of the present invention includes a touch sensingdevice. The touch sensing device senses a touch input by using touchsensors embedded in a display panel 100.

The pixels are disposed in a matrix form defined by data lines S1 to Sm(or DL1 to DLm) and gate lines G1 to Gn (or GL1 to GLn). Each of thepixels includes a pixel TFT formed at a crossing of the data lines S1 toSm and the gate lines G1 to Gn, a pixel electrode receiving a datavoltage through the pixel TFT, a common electrode to which a commonvoltage Vcom is applied, a storage capacitor Cst connected to the pixelelectrode to hold a voltage of a liquid crystal cell, and the like. Acommon electrode is separated from a plurality of touch sensors duringthe touch sensor driving period.

In the LCD device, a liquid crystal layer is formed between twosubstrates of a display panel 100. Liquid crystal molecules of theliquid crystal layer are driven by an electric field generated due to apotential difference between a data voltage applied to the pixelelectrode and the common voltage applied to the common electrode. Thepixel array of the display panel 100 includes pixels defined by datalines S1 to Sm (m is a positive integer equal to or greater than 2) andgate lines G1 to Gn (n is a positive integer equal to or greater than2), and touch sensors divided from the common electrode connected to thepixels. The touch sensors include Tx lines Tx1 to Txj (j is a positiveinteger smaller than n), Rx lines Rx1 to Rxi (i is a positive integersmaller than m) intersecting the Tx lines Tx1 to Txj, and a mutualcapacitance Cm between the Tx lines Tx1 to Txj and the Rx lines Rx1 toRxi.

The display device according to the first example embodiment of thepresent invention further includes display driving circuits 12 and 14,and a timing controller 20 for writing data of an input image to pixels,sensor driving circuits 30 and 32 driving the touch sensors, and a powersupply unit 50 generating power.

The display driving circuits 12 and 14, the timing controller 20, andthe sensor driving circuits 30 and 32 are synchronized in response to asynchronization signal Tsync. The display driving period Td and thetouch sensor driving period Tt are temporally divided as illustrated inFIG. 8.

The display driving circuits 12 and 14, and the timing controller 20write data to pixels during the display driving period Td. The displaydriving circuits 12 and 14, and the timing controller 20 supply an ACsignal in phase with a touch driving signal Tdvr to the signal lines S1to Sm and G1 to Gn during the touch sensor driving period Td asillustrated in FIGS. 11 and 12. The pixels hold a data voltage which hasbeen charged during the display driving period because pixel TFTs areturned off during the touch sensor driving period Tt. In order tominimize parasitic capacitances between the touch sensors, and the pixelsignal lines S1 to Sm and G1 to Gn during the touch sensor drivingperiod Tt, the display driving circuit supplies first and secondparasitic capacitance suppressing signals VLFD1 and VLFD2, AC signals inphase with a touch driving signal Tdrv to the pixel signal lines S1 toSm and G1 to Gn.

The display driving circuits 12 and 14 include a data driving circuit 12and a gate driving circuit 14. The data driving circuit 12 convertsdigital video data RGB of an input image received from the timingcontroller 20 into analog positive polarity/negative polarity gammacompensation voltages to output data voltages during the display drivingperiod Td. The data voltages output from the data driving circuit 12 aresupplied to the data lines S1 to Sm. The data driving unit 12 suppliesthe first parasitic capacitance suppressing signal VLFD1 to the datalines Si to Sm during the touch sensor driving period Tt. The firstparasitic capacitance suppressing signal VLFD1 is in phase with thetouch driving signal Tdrv applied to the touch sensors. The firstparasitic capacitance suppressing signal VLFD1 changes voltages at bothends of the parasitic capacitance simultaneously to minimize an amountof electric charge charged in the parasitic capacitance. A voltage levelof the first parasitic capacitance suppressing signal VLFD1 is formed tobe lower than that of the touch driving signal Tdrv so that electriccharges may be charged in the mutual capacitance.

During the display driving period Td, the gate driving circuit 14sequentially supplies a gate pulse (or scan pulse) in synchronizationwith a data voltage to select a line of the display panel 100 to whichthe data voltages are written. The gate pulse is swung between a gatehigh voltage VGH and a gate low voltage VGL. The gate pulse is appliedto the gates of the pixel TFTs through the gate lines G1 to Gn. The gatehigh voltage VGL is set to a voltage higher than a threshold voltage ofthe pixel TFTs to turn on the pixel TFTs. The gate low voltage VGL is avoltage lower than the threshold voltage of the pixel TFTs. During thetouch sensor driving period Tt, the gate driving circuit 14 supplies thesecond parasitic capacitance suppressing signal VLFD2 to the gate linesG1 to Gn. The second parasitic capacitance suppressing signal VLFD2 isin phase with the touch driving signal Tdrv applied to the touchsensors. Thus, the parasitic capacitance between the touch sensors andthe gate lines are minimized. The voltage of the AC signal applied tothe gate lines G1 to Gn during the touch sensor driving period Tt shouldbe lower than the gate high voltage VGH and lower than the thresholdvoltage of the pixel TFTs such that data written to the pixels may notbe changed.

The timing controller 20 receives timing signals such as a verticalsynchronization signal Vsync, a horizontal synchronization signal Hsync,a data enable (DE) signal, a main clock MCLK, and the like, from a hostsystem 40. The timing controller 20 synchronizes an operation timing ofthe data driving circuit 12 and the gate driving circuit 14. The timingcontroller 20 may output scan timing signals, including a gate startpulse (GSP), a gate shift clock (GSC), a gate output enable (GOE)signal, and the like. The timing controller 20 may also output datatiming control signals, including a source sampling clock (SSC), apolarity (POL) control signal, a source output enable (SOE) signal, andthe like.

The host system 40 may be implemented as any one of a television system,a set-top box (STB), a navigation system, a DVD player, a Blu-rayplayer, a personal computer (PC), a home theater system, a phone system,and other systems incorporating or in use with a display. The hostsystem 40, including a system-on-chip (SoC) with a scaler embeddedtherein, converts digital video data of an input image into a formatappropriate for the resolution of the display panel 100. The host system40 transmits the timing signals (e.g., Vsync, Hsync, DE, and MCLK),together with the digital video data RGB of the input image, to thetiming controller 20. Also, the host system 40 executes an applicationprogram associated with coordinate information (XY) of a touch inputfrom the sensing circuit 30.

The timing controller 20 or the host system 40 may generate asynchronization signal for synchronizing the display driving circuits 12and 14, the timing controller 20, and the sensing circuit 30.

The Tx lines Tx1 to Txj and the Rx lines Rx1 to Rxi may receive thecommon voltage Vcom during the display driving period Td. The touchdriving signal Tdrv is supplied to the Tx lines Tx1 to Txj during thetouch sensor driving period Td. The Tx lines Tx1 to Txj and the Rx linesRx1 to Rxi are connected to pixels through parasitic capacitances andpixel signal lines.

Sensor electrodes (e.g., C1 and C2) of a Tx line adjacent in atransverse direction (x-axis direction) may be connected through abridge pattern 101 in the pixel array or may be connected throughrouting lines (not shown) formed in a bezel region outside the pixelarray. The bridge pattern 101 connects the sensor electrodes C1 and C2of the Tx line, which are spaced apart from one another between Rx linesthrough an insulating layer.

In FIG. 7, reference numeral 11 denotes a pixel electrode. The Tx linesTx1 to Txj include sensor electrodes (e.g., C1 to C4) connected in thetransverse direction (X-axis direction). Each of the sensor electrodesC1 to C4 are patterned to have a size greater than that of a pixel andare connected to a plurality of pixels. Each of the sensor electrodes C1to C4 may be formed of a transparent conductive material, for example,indium tin oxide (ITO). The Rx lines Rx1 to Rxi may also be formed ofITO. In order to compensate for resistance of ITO, metal lines formed ofa low-resistivity metal, for example, Cu, AlNd, Mo, Ti, and the like,may be connected to the Tx lines Tx1 to Txj and the Rx lines Rx1 to Rxi,respectively.

The sensor driving circuits 30 and 32 include a sensing circuit 30 and aTx driving circuit 32. The sensor driving circuits 30 and 32 may supplythe common voltage Vcom of pixels to the Tx lines Tx1 to Txj and the Rxlines Rx1 to Rxi during the display driving period Td. The sensordriving circuits 30 and 32 supply the touch driving signal Tdrv to theTx lines Tx1 to Txj and receive electric charges from the mutualcapacitance Cm through the Rx lines Rx1 to Rxi during the touch sensordriving period Td.

After supplying the common voltage Vcom to the Tx lines Tx1 to Txjduring the display driving period, the Tx driving circuit 32 suppliesthe touch driving signal Tdrv to the Tx lines Tx1 to Txj during thetouch sensor driving period Tt. The Tx driving circuit 32 maysequentially shift the touch driving signal Tdrv. In this case, the datadriving circuit 12, the gate driving circuit 14, and the sensing circuit30 may be synchronized to shift an AC signal in phase with the touchdriving signal Tdrv.

The sensing circuit 30 provides a third parasitic capacitancesuppressing signal VLFD3 to the Rx lines Rx1 to Rxi during the touchsensor driving period Tt. The third parasitic capacitance suppressingsignal VLFD3 is in phase with the touch driving signal Tdrv. During thetouch sensor driving period Tt, the sensing circuit 30 compares theamount of change in electric charges of the touch sensors with apredetermined threshold value and senses a change in capacitance greaterthan the threshold value, as a touch input. The sensing circuit 30generates coordinate information (XY) indicating a position and an areaof each touch input and transmits the generated coordinate informationto the host system 40.

As illustrated in FIG. 11, the data driving circuit 12, and the sensordriving circuits 30 and 32 may be integrated in a single integratedcircuit (IC) and bonded to a substrate of the display panel through achip-on-glass (COG) process.

The power supply unit 50 supplies the common voltage Vcom to the touchsensors during the display driving period Td. The power supply unit 50generates power such as a gate high voltage VGH, a gate low voltage VGL,a gamma reference voltage, a logic source voltage Vcc for driving thetiming controller 20, the driving circuits 12, 14, and 32, the sensingcircuit 30, and the like. The analog positive polarity/negative polaritygamma compensation voltage is determined based on the gamma referencevoltage. The power supply unit 50 generates an AC signal voltage inphase with the touch driving signal Tdrv during the touch sensor drivingperiod Tt.

FIGS. 9 and 10 are views illustrating a driving method of a touchsensing device according to an example embodiment of the presentinvention.

As shown in FIGS. 9 and 10, during the touch sensor driving period Tt,data is written to pixels. During the display driving period Td, thecommon voltage Vcom is supplied to the pixels through the Tx lines Tx1to Txj and the Rx lines Rx1 to Rxi. During the touch sensor drivingperiod Tt, the touch driving signal Tdrv is supplied to the Tx lines Tx1to Txj, and electrical charges of the mutual capacitance Cm are receivedthrough the Rx lines Rx1 to Rxi in synchronization with the touchdriving signal Tdrv.

During the touch sensor driving period Tt, an AC signal in phase withthe touch driving signal Tdrv is supplied to the pixel signal lines inorder to minimize parasitic capacitances connected to the touch sensors.The AC signal may also be supplied to the Rx lines Rx1 to Rxi. In orderfor electric charges to be charged in the mutual capacitance Cm, thereshould be a potential difference between the Tx lines and the Rx lines.Thus, a voltage Vtx of the touch driving signal Tdrv should be higherthan voltages Vac1 and Vac2 of the AC signals respectively applied tothe pixel signal lines DL and GL, and the Rx lines.

FIG. 11 is a detailed circuit diagram illustrating the driving circuitof the display device according to an embodiment of the presentinvention. FIG. 12 is an example waveform illustrating a pixel drivingsignal and a touch driving signal output from the driving circuit ofFIG. 11. In FIG. 11, Clc denotes a liquid crystal cell, and T3 denotes apixel TFT. In FIG. 11, the driving circuit is illustrated mainly basedon a circuit that generates an AC signal in phase with the touch drivingsignal Tdrv. The Tx driving circuit 32 is omitted in the illustration.

As shown in FIGS. 11 and 12, the power supply unit 50 generates thecommon voltage Vcom, the logic source voltage Vcc, the gate high voltageVGH, the gate low voltage VGL, parasitic capacitance suppressing signalvoltages Vh1 to Vh3 and Vl1 to Vl3, and the like. The logic sourcevoltage Vcc is driving voltage of the gate driving circuit 14 and theIC.

The power supply unit 50 includes a plurality of multiplexers 51 to 53.A first multiplexer 51 selectively supplies a gate low voltage VGL1, andparasitic capacitance suppressing voltages Vh1 and Vl1 to the gatedriving circuit 14 in response to a first select signal. A secondmultiplexer 52 selectively outputs parasitic capacitance suppressingvoltages Vh2 and Vl2 in response to a second select signal. A thirdmultiplexer 53 selectively outputs parasitic capacitance suppressingvoltages Vh3 and Vl3 in response to a third select signal. The parasiticcapacitance suppressing voltages are swung between the high potentialvoltages Vh1 to Vh3 and the low potential voltages Vl1 to Vl3.

The gate high voltage VGH and the gate low voltage VGL are supplied tothe gate lines (e.g., G1 and G2) through the gate driving circuit 14.The gate driving circuit 14 sequentially shifts an output waveform byusing a shift register. In response to a gate start pulse GSP, the shiftregister outputs a gate shift clock GSC and shifts the output. An ACsignal output from the power supply unit 50 is a gate shift clock, whichis input to the shift register.

During the display driving period Td, the gate driving circuit 14supplies a gate pulse swung between the VGH and the VGL to the gatelines G1 and G2. During the touch sensor driving period Tt, the gatedriving circuit 14 supplies the second parasitic capacitance suppressingsignal VLFD2 swung between the voltages Vh1 and Vl1 in synchronizationwith the touch driving signal Tdrv to the gate lines G1 and G2. Vh1 islower than VGH and lower than a threshold voltage of the pixel TFTs T3.

During the display driving period Td, the IC supplies the common voltageVcom input from the power supply unit 50 to the Tx lines Tx1 to Txj andthe Rx lines Rx1 to Rxi. During the touch sensor driving period Tt, theIC supplies the touch driving signal Tdrv to the Tx lines Tx1 to Txj andsupplies the first to third parasitic capacitance suppressing signalsVLFD1, VLFD2, and VLFD3 received from the power supply unit 50 to thepixel signal lines S1 to Sm and G1 to Gn, and the Rx lines Rx1 to Rxi,respectively.

The IC includes a plurality of multiplexers 13 and 33 coupled to thedata driver 12 and the sensing circuit 30, respectively. Fourthmultiplexers 33 each include an output terminal connected to arespective one of the Rx lines Rx1 to Rxi and input terminalsrespectively connected to the sensing circuit 30 and the secondmultiplexer 52. In response to a fourth select signal, the fourthmultiplexers 33 supply the common voltage Vcom input from the sensingcircuit 30 to the Rx lines Rx1 to Rxi during the display driving periodTd. The fourth multiplexers 33 supply the third parasitic capacitancesuppressing signal VLFD3 supplied through the second multiplexer 52 tothe Rx lines Rx1 to Rxi during the touch sensor driving period Tt.During the touch sensor driving period Tt, the sensing circuit 30receives electric charges of the mutual capacitance Cm through the Rxlines Rx1 to Rxi to which the third parasitic capacitance suppressingsignal VLFD3 is supplied and the fourth multiplexers 33.

Fifth multiplexers 13 each include an output terminal connected to arespective one of the data lines DL1 to DLn and input terminalsrespectively connected to the data driving circuit 12 and the thirdmultiplexer 53. During the display driving period Td, in response to afifth select signal, the fifth multiplexers 13 supply a data voltage ofan input image output from the data driving circuit 12 to the data linesDL1 to DLm. Thereafter, during the touch sensor driving period Tt, thefifth multiplexers 13 supply an AC signal to the data lines DL1 to DLm.

The timing controller 20 or a micro-controller unit (MCU) of the sensingcircuit 30 may generate select signals for controlling the first tofifth multiplexers 51, 52, 53, 13, and 33.

As discussed above, the touch sensing device according to an exampleembodiment of the present invention can minimize parasitic capacitancepresent in the panel by using the first to third parasitic capacitancesuppressing signals VLFD1 to VLFD3 respectively provided to the datalines S1 to Ln (or DL1 to DLn), the gate lines G1 to Gm (or GL1 to GLm),and the Rx lines Rx1 to Rxi during the touch sensor driving period Td.Preferably, the first to third parasitic capacitance suppressing signalsVLFD1 to VLFD3 should make parasitic capacitances present in the panel‘zero’. However, due to the panel characteristics, a reduced amount ofparasitic capacitances may still remain in the panel even after thefirst to third parasitic capacitance suppressing signals VLFD1 to VLFD3are applied.

Thus, in order to exclude an influence of parasitic capacitances thatremain in the panel even after the use of the first to third parasiticcapacitance suppressing signals VLFD1 to VLFD3, the touch sensing deviceaccording to an example embodiment of the present invention varies avoltage level of the parasitic capacitance suppressing signal VLFD.

FIG. 13 is a flow chart illustrating an example process of setting avoltage level of a parasitic capacitance suppressing signal VLFD, andFIG. 14 is a view illustrating an example sensing circuit according toan embodiment of the present invention. A process of setting a voltagelevel of the parasitic capacitance suppressing signal VLFD according toan example embodiment of the present invention will be described withreference to FIGS. 5 through 14.

In order to set a voltage level of the parasitic capacitance suppressingsignal VLFD, the display driving circuits 12, 14, and 20 provides firstto third parasitic capacitance suppressing signals VLFD1 to VLFD3 to thepixel lines, respectively. Namely, the display driving circuits 12 and14, and the timing controller 20 provide the first parasitic capacitancesuppressing signal VLFD1 to the data lines S1 to Sm, the secondparasitic capacitance suppressing signal VLFD2 to the gate lines G1 toGn, and the third parasitic capacitance suppressing signal VLFD3 to theRx lines Rx1 to Rxi. All of the first to third parasitic capacitancesuppressing signals VLFD1 to VLFD3 have an identical voltage level,before their voltage levels are corrected.

The sensing circuit 30 calculates parasitic capacitances remaining inthe panel based on a change in an output value according to the first tothird parasitic capacitance suppressing signals VLFD1 to VLFD3. Thesensing circuit 30 may include an integrator such as the one illustratedin FIG. 14. The integrator may receive a reference voltage V_(MOD), andoutputs an output value increased in proportion to parasiticcapacitance, to an output terminal O. An output Vout output by theintegrator is expressed as Equation 1 below.

Vout=(Cp/Cf)×V _(MOD)  [Equation 1]

Here, Cp denotes the panel capacitance based on the parasiticcapacitance suppressing signals, Cf denotes the overall capacitance ofthe panel, and V_(MOD) denotes the reference voltage input to theintegrator. The reference voltage V_(MOD) is an AC signal in phase withthe first to third parasitic capacitance suppressing signals VLFD1 toVLFD3.

As mentioned above, preferably, parasitic capacitances remaining in thepanel should be removed when the first to third parasitic capacitancesuppressing signals VLFD1 to VLFD3, and thus, the output value Voutshould be 0. In other words, if the output value Vout is not 0, it meansthat parasitic capacitance remains in the panel even after the first tothird parasitic capacitance suppressing signals VLFD1 to VLFD3 areapplied.

If parasitic capacitance remains in the panel even after the first tothird parasitic capacitance suppressing signals VLFD1 to VLFD3 areapplied, it means that a relative potential of a portion correspondingto pixel lines to which the first to third parasitic capacitancesuppressing signals VLFD1 to VLFD3 are provided, has been increased.Thus, in order to remove an influence of the parasitic capacitanceremaining even after the first to third parasitic capacitancesuppressing signals VLFD1 to VLFD3 are applied, the sensing circuit 30increases voltage levels of the first to third parasitic capacitancesuppressing signals VLFD1 to VLFD3 in proportion to the remainingparasitic capacitance.

For example, the sensing circuit 30 may set voltage levels of the firstto third parasitic capacitance suppressing signals VLFD1 to VLFD3 tosatisfy conditions of Equation 2 below.

VLFDH=V _(MOD)×{1+(Cp _(—) r/Cp _(—) t}  [Equation 2]

Here, VLFDH denotes voltage levels of the first and second parasiticcapacitance suppressing signals, V_(MOD) denotes the reference voltage,Cp_r denotes a remaining parasitic capacitance of the panel, and Cp_tdenotes a total parasitic capacitance of the panel.

In this manner, since the sensing circuit 30 increases the voltagelevels of the first to third parasitic capacitance suppressing signalsVLFD1 to VLFD3 in proportion to the remaining parasitic capacitance, aninfluence of the parasitic capacitance remaining even after the first tothird parasitic capacitance suppressing signals VLFD1 to VLFD3 areapplied, on the touch sensing process may be prevented.

FIG. 15 is a view illustrating a configuration of a touch sensing deviceaccording to a second example embodiment of the present invention, FIG.16 is a schematic view illustrating a connection between a touch sensorTs and a sensing unit 130 of a display panel according to the secondexample embodiment of the present invention. FIG. 17 is an equivalentcircuit diagram illustrating parasitic capacitance in a self-capacitancesensor structure.

The touch sensing device according to the second example embodiment ofthe present invention includes a display panel 100, a data driving unit12, a gate driving unit 14, a timing controller 20, and a sensing unit130. The same reference numerals will be used for the componentssubstantially identical to those of the example embodiments describedabove, and a detailed description thereof will be omitted.

Self-capacitance Cs is formed by touch sensors Ts divided from a commonelectrode. The touch sensors Ts are connected to sensor lines L1 to L4,respectively. Electrode patterns or touch sensor patterns may be formedof a transparent metal, such as indium tin oxide (ITO). The sensor linesL1 to L4 may be formed of a low-resistivity metal, such as copper (Cu).A touch sensor driving unit includes a charge pump (not shown) and thesensing unit 130. The charge pump supplies electric charges to aself-capacitance Cs from the touch sensors Ts through the sensor linesL1 to L4, respectively. The sensing unit 130 includes an analog circuitand an analog-to-digital converter (ADC). The analog circuit receiveselectric charges from the self-capacitance Cs and outputs an amount ofchange in electric charges before and after an applied touch, as ananalog voltage. The ADC converts the analog voltage input from theanalog circuit into digital data, and outputs touch low data.

In FIG. 17, C1 to C8 denote parasitic capacitances formed between thelines and electrodes. Namely, C1 is a parasitic capacitance between thetouch sensor Ts and the gate line GL, and C2 is a parasitic capacitancebetween the touch sensor Ts and the data line DL. C3 is a parasiticcapacitance between the sensor line L and the gate line GL, and C4 is aparasitic capacitance between the sensor line L and the data line S. C5and C6 are parasitic capacitances between adjacent touch sensors Ts. C7is a parasitic capacitance between the touch sensor Ts and otherelectrode lines, C8 is parasitic capacitance between the data line DLand the gate line GL.

The data lines DL1 to DLm receive a first parasitic capacitancesuppressing signal VLFD1 during a touch sensor driving period Tt. Thegate lines GL1 to GLn receive a second parasitic capacitance suppressingsignal VLFD2 during the touch sensor driving period Tt. The first andsecond parasitic capacitance suppressing signals VLFD1 and VLFD2 changevoltages at both ends of each parasitic capacitance to minimize anamount of electric charges charged in each parasitic capacitance.Namely, the first and second parasitic capacitance suppressing signalsVLFD1 and VLFD2 simultaneously change total voltages at both ends of theparasitic capacitances, i.e., the sum of C1 to C8.

Also, like the first and second parasitic capacitance suppressingsignals VLFD1 and VLFD2 according to the first example embodiment of thepresent invention described above, the first and second parasiticcapacitance suppressing signals VLFD1 and VLFD2 according to the secondexample embodiment of the present invention are varied in proportion tothe remaining parasitic capacitance. A process of varying voltage levelsof the first and second parasitic capacitance suppressing signals VLFD1and VLFD2 is the same as that of the first example embodiment of thepresent invention.

In the present invention, during the touch driving period, a touchdriving signal may be applied to the Tx lines and, simultaneously, aparasitic capacitance suppressing signal as an AC signal in phase withthe touch driving signal may be supplied to the pixel signal lines tominimize an influence of parasitic capacitances connected to the touchsensors.

In particular, in the present invention, in a case in which a parasiticcapacitance remains even after a parasitic capacitance suppressingsignal is provided, a voltage level of the parasitic capacitancesuppressing signal is varied in proportion to the remaining parasiticcapacitance. Accordingly, an influence of the remaining parasiticcapacitance on the sensing operation can be prevented or furtherreduced.

By using the parasitic capacitance suppressing signal, a touch screen ofthe display device including in-cell touch sensors can be increased insize, and its resolution can be enhanced.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the touch sensing device anddriving method of the present invention without departing from thespirit or scope of the invention. Thus, it is intended that the presentinvention cover the modifications and variations of this inventionprovided they come within the scope of the appended claims and theirequivalents.

What is claimed is:
 1. A touch sensing device comprising: a panelincluding pixels disposed in a matrix form defined by data lines andgate lines, the pixels including thin film transistors (TFTs); at leastone touch sensor having a mutual capacitance; a sensor driving circuitconfigured to receive an electric charge from the mutual capacitance;and a display driving circuit configured to supply a first parasiticcapacitance suppressing signal to the data lines and a second parasiticcapacitance suppressing signal to the gate lines during a touch sensordriving period.
 2. The touch sensing device of claim 1, wherein thedisplay driving circuit is configured to provide the first and secondparasitic capacitance suppressing signals to the data lines in phasewith a touch driving signal, and to set voltage levels of the first andsecond parasitic capacitance suppressing signals in proportion to anoverall parasitic capacitance of the panel.
 3. The touch sensing deviceof claim 2, wherein the voltage levels of the first and second parasiticcapacitance suppressing signals are lower than a voltage of the touchdriving signal.
 4. The touch sensing device of claim 1, wherein thesensor driving circuit comprises an integrator configured to output anoutput voltage based on a remaining parasitic capacitance of the panelafter the application of the first and second parasitic capacitancesuppressing signals, and on a reference voltage, wherein the displaydriving circuit is configured to modify a voltage level of at least oneof the first and second parasitic capacitance suppressing signals basedon the remaining parasitic capacitance of the panel calculated and onthe output voltage from the integrator.
 5. The touch sensing device ofclaim 4, wherein the display driving circuit is configured to modify thevoltage level of at least one of the first and second parasiticcapacitance suppressing signals based on an equation:V _(LFDH) =V _(MOD)×{1+(Cp _(—) r/Cp _(—) t)}, wherein VLFDH denotes amodified voltage level of at least one of the first and second parasiticcapacitance suppressing signals, V_(MOD) denotes the reference voltage,Cp_r denotes the remaining parasitic capacitance of the panel, and Cp_tdenotes a total parasitic capacitance of the panel.
 6. The touch sensingdevice of claim 1, wherein the at least one touch sensor includes themutual capacitance disposed between a touch sensor transmission line anda touch sensor reception line intersecting each other, and wherein thesensor driving circuit is configured to provide a third parasiticcapacitance suppressing signal in phase with the first and secondparasitic capacitance suppressing signals to the touch reception lineduring the touch sensor driving period.
 7. The touch sensing device ofclaim 6, wherein the gate pulse is swung between a gate high voltagehigher than a threshold voltage of the TFTs and a gate low voltage lowerthan the threshold voltage of the TFTs, and the voltage of at least oneof the first, second, and third parasitic capacitance suppressingsignals is lower than the gate high voltage.
 8. The touch sensing deviceof claim 1, wherein the panel includes the at least one touch sensor. 9.A touch screen display device comprising: a display panel including atleast one touch sensor having a mutual capacitance and pixels disposedin a matrix form defined by data lines and gate lines, the pixelsincluding thin film transistors (TFTs); a sensor driving circuitconfigured to receive an electric charge from the mutual capacitance;and a display driving circuit configured to supply a data voltage of aninput image to the data lines and a gate pulse to the gate lines duringa display driving period, and to supply a first parasitic capacitancesuppressing signal to the data lines and a second parasitic capacitancesuppressing signal to the gate lines during a touch sensor drivingperiod.
 10. The touch screen display device of claim 9, wherein thedisplay driving circuit is configured to provide the first and secondparasitic capacitance suppressing signals to the data lines in phasewith a touch driving signal, and to set voltage levels of the first andsecond parasitic capacitance suppressing signals in proportion to anoverall parasitic capacitance of the display panel.
 11. The touch screendisplay device of claim 10, wherein the voltage levels of the first andsecond parasitic capacitance suppressing signals are lower than avoltage of the touch driving signal.
 12. The touch screen display deviceof claim 9, wherein the sensor driving circuit comprises an integratorconfigured to output an output voltage based on a remaining parasiticcapacitance of the panel after the application of the first and secondparasitic capacitance suppressing signals, and on a reference voltage,wherein the display driving circuit is configured to modify a voltagelevel of at least one of the first and second parasitic capacitancesuppressing signals based on the remaining parasitic capacitance of thepanel calculated and on the output voltage from the integrator.
 13. Thetouch screen display device of claim 12, wherein the display drivingcircuit is configured to modify the voltage level of at least one of thefirst and second parasitic capacitance suppressing signals based on anequation:V _(LFDH) =V _(MOD)×{1+(Cp _(—) r/Cp _(—) t)}, wherein VLFDH denotes amodified voltage level of at least one of the first and second parasiticcapacitance suppressing signals, V_(MOD) denotes the reference voltage,Cp_r denotes the remaining parasitic capacitance of the panel, and Cp_tdenotes a total parasitic capacitance of the panel.
 14. The touch screendisplay device of claim 9, wherein the at least one touch sensorincludes the mutual capacitance disposed between a touch sensortransmission line and a touch sensor reception line intersecting eachother, and wherein the sensor driving circuit is configured to provide athird parasitic capacitance suppressing signal in phase with the firstand second parasitic capacitance suppressing signals to the touchreception line during the touch sensor driving period.
 15. The touchscreen display device of claim 14, wherein the gate pulse is swungbetween a gate high voltage higher than a threshold voltage of the TFTsand a gate low voltage lower than the threshold voltage of the TFTs, andthe voltage of at least one of the first, second, and third parasiticcapacitance suppressing signals is lower than the gate high voltage. 16.A method of driving a touch sensing device having a panel with at leastone touch sensor and pixels disposed in a matrix form defined by datalines and gate lines, the method comprising: supplying a first parasiticcapacitance suppressing signal to the data lines and a second parasiticcapacitance suppressing signal to the gate lines; determining aremaining amount of electric charge in the panel; and if the remainingamount of electric charge exceeds a threshold amount, modifying avoltage level of at least one of the first and second parasiticcapacitance suppressing signals based on the remaining parasiticcapacitance.
 17. The method of claim 16, wherein the threshold amount iszero.
 18. The method of claim 16, wherein the modifying includes settingthe voltage level of at least one of the first and second parasiticcapacitance suppressing signals based on an equation:V _(LFDH) =V _(MOD)×{1+(Cp _(—) r/Cp _(—) t)}, wherein VLFDH denotes amodified voltage level of at least one of the first and second parasiticcapacitance suppressing signals, V_(MOD) denotes a reference voltage,Cp_r denotes the remaining parasitic capacitance of the panel, and Cp_tdenotes a total parasitic capacitance of the panel.